An extensive prior art exists which deals with solving the problem of cooling off a tool holder that has previously been heated in order to shrink-release it from or shrink-fit it into a tool.
Roughly summarized, three different cooling principles have so far been proposed. These are air cooling, liquid cooling and cooling by solid-body contact, i.e. by intimately bringing into contact the surface of the tool holder to be cooled with a highly heat-conductive cooling body into which the heat dissipates.
The European patent application EP 1 138 422 A2 as well as, for example, the Japanese patent JP 2002079426 propose an air cooling process that is realized by the heated tool holder being exposed to the strong cooling air stream of a fan. A cooling air stream is capable of cooling the tool holder very uniformly and gently so that there is no danger that the tool holder, which is initially about 300° to 400° hot in places, is distorted by the cooling process. However, it is one drawback of any air cooling that the cooling process progresses comparatively slowly and therefore requires a considerable amount of time.
The French patent application FR 2 844 734 proposes a device for cooling the tool holder primarily by solid-body cooling—a cooling ring is put over the hot sleeve section of the tool holder, the inner surface of said ring intimately abutting against the sleeve section and withdrawing heat from it by thermal conduction, which is then released to the outside by the cooling ring via its cooling fins which are situated in the cooling air stream. Compared to conventional air cooling, the cooling ring thus increases the surface that the cooling air effectively sweeps over.
Such a cooling ring has to be put on and removed again, thus requiring an additional working step which costs time and thus negates the advantage of a faster cooling-off process than in the case of direct fanning of the tool holder. Even more serious is the problem that the sleeve sections of the various tool holders to be cooled have different diameters or contours and that therefore an entire set of different cooling rings has to be kept in store, because the cooling ring principle only works if the cooling ring is able to adapt intimately to the respective sleeve section. Thus, not only is an increased material, storage and supply expenditure required, rather, the fitting cooling ring also has to be selected in each case manually or by means of correspondingly extensive technical equipment. Furthermore, the maximum achievable cooling performance of such a system is naturally limited by the thermal conductivity of the cooling body. Consequently, the cooling performance is limited particularly if the cooling body is not used instationarily (i.e. is heated up from an initially cold state), but if it has to cool down various tool holders directly one after the other.
The German patent applications DE 103 20 641 A1 and DE 10 2007 000 906 A1 each propose liquid cooling in the form of a submersion bath into which the heated tool holder is lowered. In this way, the heated tool holder is in each case cooled off very rapidly. However, this time advantage is negated again to a large extent by the completely or extensively wetted tool holder having to be dried off again in a subsequent step (already in order to avoid corrosion) before it can be stored. Furthermore, such an abrupt cooling-off always entails the risk of the tool holder being distorted, and places considerable stress on the tool holder also if the tool holder is not distorted immediately.
Patent applications EP 1 584 408 A1 and WO 2007/028522 A2 propose liquid cooling by sprinkling or spraying the tool holder to be cooled off with a liquid coolant. In both cases, three perforated pipes are provided which are disposed distributed laterally next to and around the chuck to be cooled off, wherein a coolant jet is discharged directly onto the chuck from each of the holes. Naturally, this coolant jet has to be strong enough for sufficiently wetting the entire surface to be cooled by it (namely a third of the outer circumference to be cooled off).
Such a direct sprinkling or spraying is advantageous in that the tool holder to be cooled off is cooled off rapidly, but not too abruptly. However, there is still the problem also in this case that it is practically impossible to cool off the tool holder just as uniformly as, for example, by means of air cooling. For it is inevitable, even if the nozzles discharging the coolant are disposed uniformly about the tool holder, that certain sections of the tool holder are sprinkled or sprayed with the coolant to a greater extent than other sections.
In the case of such a cooling by means of direct sprinkling or spraying, there is still the danger of the tool holder being distorted, even if it is only by a small amount, which would not be a bother in components other than a tool holder, which is subject to the highest requirements with regard to its running properties. Moreover, there is still the problem that it is possible only to a rudimentary extent to vary the cooling performance—for example WO 2007/028522 A2 proposes to switch the coolant nozzles on and off in an interval-like manner in order to be able to influence the cooling rate at least slightly.
Furthermore, the tool holder is intensively wetted with the liquid coolant by direct spraying and therefore has to be dried first for a longer period of time subsequent to the cooling-off process.
Finally, such cooling exclusively by direct sprinkling or spraying of the coolant is disadvantageous in that, in the initial phase of the cooling-off process, when the tool holder is still very hot, a not inconsiderable part of the coolant evaporates and possibly escapes into the environment, or that it has to be collected using separate measures in order not to pollute the environment.
Finally, it should be noted that, generally, there is always the problem, in all those devices from the prior art that use liquid coolants, that special measures have to be taken to drain off or collect the coolant, which rather slowly runs down the tool holder after the tool holder has been pulled out of the submersion bath again or after the spraying has been switched off.
In view of this, the invention is based on the object of providing a cooling device which is capable of causing a significantly more rapid cooling than those cooling devices that are based on the air cooling principle, but in which, in contrast to the hitherto known cooling devices that use water cooling, there is no danger of too-rapid or non-uniform cooling. Preferably, the cooling device according to the invention is supposed to achieve the object especially also where shrink chucks are to be cooled off.